Williams was “unconscious and not breathing” when emergency workers arrived at his house in Tiburon in response to a 911 call about 11:55 a.m. local time, according to the Marin County Sheriff’s Office.

He was pronounced dead at 12:02 p.m.

“At this time, the Sheriff’s Office Coroner Division suspects the death to be a suicide due to asphyxia, but a comprehensive investigation must be completed before a final determination is made,” Lt. Keith Boyd said in a prepared statement.

Early Tuesday, Oakland TV station KTVU reported that a source close to the investigation said the actor hanged himself.

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Williams, who married three times and had three adult children, was last seen alive Sunday evening in the home he shared with his wife, graphic designer Susan Schneider.

Robin Williams holds up his Oscar after winning in the Best Actor in a Supporting Role category during the 70th Academy Awards.Photo: Getty Images

His body was found by unspecified family members, the San Francisco Chronicle reported.

“This morning, I lost my husband and my best friend, while the world lost one of its most beloved artists and beautiful human beings. I am utterly heartbroken,” Schneider said in a statement.

“On behalf of Robin’s family, we are asking for privacy during our time of profound grief. As he is remembered, it is our hope the focus will not be on Robin’s death, but on the countless moments of joy and laughter he gave to millions.”

His publicist, Mara Buxbaum, said Williams had “been battling severe depression of late.”

Last year, Williams returned to the small screen after more than 30 years as a movie actor, telling Parade magazine that he needed a “steady job.”

“The movies are good, but a lot of times they don’t even have distribution,” he said. “There are bills to pay.”

Asked whether he had lost “all his money” to his exes, Williams said, “Well, not all,” before adding: “Divorce is expensive.”

But CBS canceled his comedy series “The Crazy Ones” in May after just one season.

The frenetic funnyman shot to stardom after a 1978 guest appearance on TV’s “Happy Days” led to the hit spinoff “Mork and Mindy,” on which he played an outer-space alien sent from the planet Ork to observe life on Earth.

Williams ended each show by calling Ork’s leader, Orson, to report his findings, and Mork’s trademark greeting “Na-nu, Na-nu” and expletive “Shazbot” both became popular catchphrases of the time.

Williams also appeared in a series of HBO stand-up comedy specials that showcased his quirky, rapid-fire humor and impressions, as well as dozens of feature films.

In 1998, he won an Oscar as Best Supporting Actor as a therapist in “Good Will Hunting,” after failing to take home the prize in three previous best-actor nominations, for “Good Morning, Vietnam,” “Dead Poets Society” and “The Fisher King.”

One of his most iconic roles was as the cross-dressing divorced dad in the 1993 hit “Mrs. Doubtfire,” which he was reportedly set to reprise in an upcoming sequel.

He recently completed work on two holiday-season releases — “Night at the Museum: Secret of the Tomb” and the indie family comedy “Merry Friggin’ Christmas” — and voiced the animated character Dennis the Dog in “Absolutely Anything,” due out next year.

He also co-starred with Bob Odenkirk of TV’s “Breaking Bad” in the drama “Boulevard.”

But Williams’ seemingly charmed life was beset by personal problems, including a cocaine addiction early in his career that provided grist for his stand-up routine, including jokes such as “Cocaine is God’s way of saying that you’re making too much money.”

In 1982, Williams infamously partied with wild-man comic John Belushi hours before the “Saturday Night Live” icon died of a heroin-and-cocaine overdose.

Williams’ marital infidelity also led him to divorce first wife Valerie Velardi and marry their son Zach’s nanny, Marsha Garces, who was pregnant with his daughter, Zelda.

A photo posted by therobinwilliams (@therobinwilliams) on Jul 31, 2014 at 4:35pm PDT

They would later have a son, Cody. But Williams divorced Garces in 2008 and married his third wife, Schneider, in 2011.

Although he quit drinking and drugs cold-turkey before the birth of his eldest child in 1983 — and stayed sober for two decades — Williams relapsed and started drinking again while working on location in Alaska in 2003. Williams went to rehab in 2006 and later blamed his alcoholism for the failure of his marriage to Garces.

Last month, Williams checked himself into the Hazelden Addiction Treatment Center in Lindstrom, Minn.